Adsorption and dissociation of hydrogen molecule on carbon nanotubes

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Abstract

Earlier, it has been suggested that carbon nanotubes can provide high storage
capacity and other physical properties suitable for the fuel cell technologies. In
this thesis we have investigated adsorption, desorption and dissociation of hydrogen
molecule on the surface of the zigzag (8,0) single-wall carbon nanotube
(SWNT) by carrying out extensive first-principles pseudopotential plane wave
calculations within the Density Functional Theory (DFT). We found that while
H2 molecule cannot be bound to the surface of bare SWNT, an elastic radial
deformation leading to the elliptical deformation of the circular cross-section renders
the physisorption of the molecule possible. Coadsorption of Li atom on the
SWNT makes the similar effect, and hence enhances the physisorption. That an
adsorbed H2 can be desorbed upon releasing the elastic radial strain is extremely
convenient for the storage. In addition to that, we found that a Pt atom coadsorbed
on the SWNT can form a strong chemisorption bond with a H2 molecule.
If a single H2 molecule engages in interactions with more than one coadsorbed
Pt atom at its close proximity it dissociates into single H atoms, which, in turn,
make Pt-H bonds. The interaction between H2 and coadsorbed Pd atom is similar
to Pt, but it is weaker. We believe that these findings clarify earlier controversial
results related to the storage of H2 in carbon nanotubes, and makes important
contributions to fuel cell technology.